Rock, dense earth, concrete, and similar materials may be broken or cracked with explosive force inside a borehole drilled into the material. One simple method of rock breaking with explosives is to make a hole, insert an explosive charge, and detonate it. Since the hole is not closed, gas escapes from the hole and the pressure drops unless high explosive is used. If low explosives are used, other methods are helpful.
Watson et al., in U.S. Pat. No. 5,308,149, discuss two prior art methods: the "gas injector method" in which a pipe is inserted into a borehole, sealed against the rock near the bottom, and then a charge is fired in from outside; and the "hole bottom pressurization" method, in which a charge is exploded at the bottom of a borehole while a massive bar is in the borehole. The bar largely plugs the hole and prevents most gas leakage. The Watson device uses a high-inertia stemming bar 3, a shaped-charge cartridge 5, and firing means 2. Watson mentions various bar sealing techniques at col. 3, line 40.
U.S. Pat. No. 4,900,092 to Van Der Westhuizen et al discloses a rock-breaking gun in which a cartridge is fired in the external end of a heavy barrel inserted into a borehole. The barrel is tapered to seal against the lip of the borehole. The barrel screws onto a firing chamber 4 to seal the charge. A mat is used to restrain the recoil. The borehole is filled with water.
U.S. Pat. No. 4,572,075 to Day et al shows blasting in water in a borehole.
Church, in U.S. Pat. No. 2,866,508 discloses firing explosive charges 20 in a borehole in conjunction with resilient seals 12 and 26. A firing pin and percussion cap 22 are used.
U.S. Pat. No. 4,185,702, issued to Bullard, shows a drilling apparatus using a muzzle-loading gun with black powder charge to propel a bullet into the earth.
Leperre in U.S. Pat. No. 4,470,352 and Marz in U.S. Pat. No. 4,492,165 disclose specialized explosive cartridges.
The device of Sloevsky et al, disclosed in U.S. Pat. No. 3,960,082, is an explosive powered rock breaker. A pipe inserted into a borehole carries an explosive charge at the external end and a cap with openings on the internal end. The interior of the pipe is filled with water, which carries the explosive force from the charge to the cap, whence it issues through radial passages 11.
Hutton, U.S. Pat. No. 1,571,122, shows an explosive cartridge fired by a primer struck by a long firing pin 20 that extends through a rod. The firing pin is held from the primer by a spring, and fires the primer when released from being pulled back against a second spring. The firing pin includes an eye 25 for pulling and releasing it. Hutton does not disclose a hammer for hitting the firing pin.
The prior art does not disclose the use a cartridge (combined explosive and primer) in a firing chamber at the internal end of a rod or bar inserted into a borehole. Neither does the prior art disclose any use of conventional firearm ammunition as a charge for breaking rock, excavating, or the like. Prior-art device do not show bars or rods inserted into a borehole that include rugged, simple, and forceful frictional holding means that bear against the side of a borehole and which are not activated by an exploding charge.
The disadvantages of the prior art are as follows:
1. Many prior-art devices require that the borehole be filed with a liquid, such as water, to transmit the shock and energy to the rock. The requirement to have the hole full of water makes the method difficult or impossible to use in upslanted holes, leaky holes, etc. PA1 2. The devices do not have a method of locking the tool in the hole before the device is fired. Sloevsky and others have a momentary lock that is powered by the pressure at the instant of detonation but does not operate before or after the pulse. This also makes it impossible to use in up holes or upslanting holes where the tool can fall out by gravity. PA1 3. The location of the cartridge in a chamber outside of the hole and the need to transmit the pressure pulse through the tool causes great stress to the mechanical parts and can eventually lead to failure. This design does not allow the explosive force to be concentrated at the bottom of the hole which diminishes its breaking power. PA1 4. Prior-art devices do not allow a projectile to be fired in the hole to generate fractures and so enhance the breaking power of the tool at the same time that the pressure of sealed explosive gases is used.